1. Field of the Invention
The present invention relates to devices and methods for machining a transparent medium, and more particularly, to devices and methods for machining a transparent medium by a laser, in which a transparent medium having a high hardness and poor in light absorption is cut or has characters or figures written into by a laser beam.
2. Background of the Related Art
Media having high hardness and transparent to light, such as glass, sapphire, silicon carbide (SiC) have a wide variety of applications, such as various windows, optical devices, LCD (liquid Crystal Display), PDP (Plasma Display Panel), and different fine tuning instruments which require high resistance to wear. Additionally, materials such as sapphire and silicon carbide are widely used as substrate materials of optical devices, such as visible (red, green, and blue and etc.) light emitting diode, laser diode, and electronic devices, such as HBT (hetero-bipolar transistor) and FET (Field Effect Transistor). Therefore, a machining technology for ready and easy cutting of those materials or writing characters or figures therein is an important technology having a great influence to the industrial fields. In the past, material with a high hardness has been processed mechanically or optically. In mechanical machining, a cutting tool of a material tougher than a workpiece, such as a diamond tip or diamond blade, is used. In optical machining, a thermal energy of light, such as a laser beam, is used.
A related art device and method for machining a transparent medium will be explained with reference to attached drawings. FIG. 1 schematically illustrates cutting a glass substrate using a related art diamond tip, and FIG. 2 schematically illustrates cutting a glass substrate using a related art diamond blade.
Referring to FIG. 1, in the cutting of a transparent medium using a related art diamond tip, a workpiece, such as glass plate 1 with a high hardness, is scribed with the diamond tip 2, to make a scratch 3 in the glass plate 1, and has a mechanical stress applied thereto, for breaking the glass plate 1 into two pieces along the scratch 3.
And, referring to FIG. 2, in the cutting of a transparent medium using a related art diamond blade, a disk of diamond blade 4 is rotated at a high speed, and workpiece such as a glass plate 5 is moved against the diamond blade 4 to wear off the glass plate 5 along a cutting line, thereby cutting the glass plate 5. In this instance, since the diamond blade 4 rotated at a high speed, fine powder of glass and the like is emitted. Fluid, such as water or oil, is sprayed to the cutting portion using a nozzle 7, for preventing powder emission.
FIG. 3 schematically illustrates cutting a glass plate with a carbon dioxide laser, and FIG. 4 schematically illustrates additional use of a supplementary frame and a gas ejecting nozzle for the cutting of a glass plate with a carbon dioxide laser.
Referring to FIG. 3, in using the laser, a laser beam 9 from a laser 8 is focused onto a workpiece 11 by a lens 10, while the workpiece 11 is moved, to melt the workpiece 11 along a cutting line 12. The laser 8 should provide a laser beam of a wavelength which can be well absorbed by the workpiece 11 according to the absorption property of the workpiece 11 material. In this instance, the transparent medium may be processed with supplementary devices added thereto, such as a supplementary frame 13 with a good thermal conductivity placed along the cutting line to set up a direction of heat dissipation and to minimize cracking of the medium in random directions. A fine nozzle 14 blows a gas to the cutting portion to blow down molten material.
Because the related art transparent media machining methods should be employed appropriately considering properties of the workpiece and cost involved, a method with a good workability and better cost should be selected considering advantages/disadvantages of the different methods in various fields.
However, the related art devices and methods for machining a transparent medium have the following problems.
First, the simplest and oldest method, in which a scratch is made in the workpiece with a related art diamond tip and a mechanical stress is applied to the workpiece to break the workpiece into two, which has been developed in many ways from a small tool for manual scratching a line and breaking the workpiece to a large scale equipment, has problems with breaking the workpiece into two pieces because the scratch is insufficiently deep, causing difficulty in breaking along the scratch. Particularly, if the medium is sapphire or silicon carbide (SiC), the workpiece to be cut should be below a certain thickness; if the thickness is greater than permitted (in a range of 100 .mu.m in cases of optical devices or electronic devices), the breaking after the scribing is more difficult due to a hardness of the workpiece medium. To obtain an appropriately thin thickness, a complicated and careful lapping, a process ahead of the breaking, is required. Moreover, the bending caused by the thin thickness adds difficulty to the breaking.
Second, periodical change of the diamond tip is required for workpieces with high hardness, such as glass plate, cut with the diamond tip, causing additional cost increase. Particularly, scribing and breaking equipment have high costs.
Third, the related art mechanical methods have difficulty in cutting a curved line inherent in this method, and a low speed. Therefore, it is not suitable for scribing characters or figures other than cutting plates. Further, the workpiece or the equipment should be aligned along a crystal direction, and a direction of the scribing and breaking should be determined, accordingly.
Fourth, although the related art method of using diamond blade can cut a comparatively thick medium, the diamond blade causes great physical damage to the workpiece with a poor cut surface. Because a blade thickness can not be reduced below a certain limit, and more material of the workpiece is consumed than the blade thickness a low productivity (i.e., a number of chips per unit area) results. Therefore, application of this method to fine cutting line applications is difficult. Moreover, the related art method of using a diamond blade has a very slow cutting speed, with a poor production rate, and creates dust requiring water spray using the nozzle 7 as shown in FIG. 2.
Fifth, though the method of cutting with a laser beam which is absorbed well can cut the workpiece in a desired form, there is a high probability of failure in the cutting due to random cracking occurred in the workpiece caused by local heating when performed at room temperature. Therefore, the workpiece should be kept close to a softening temperature during cutting, or, as shown in FIG. 4, supplementary devices should be used, such as a supplementary frame with a good thermal conductivity placed along the cutting line to set up a direction of heat dissipation, minimizing cracking of the medium in random directions, and a fine nozzle for blowing a gas to the cutting portion should be used to blow down molten material.
Sixth, since the carbon dioxide gas laser used mostly in cutting a glass plate is difficult to focus into an area smaller than a few hundred micrometers, the carbon dioxide gas laser has a limitation in fine cutting. And, as a laser should be used which is absorbed well to the workpiece medium without fail, a laser which is absorbed well to the workpiece medium is additionally required for cutting a transparent medium, even if a small sized solid state laser of a visible light range or a near infrared ray range which are used frequently in the industrial field.